linux-kernel - [PATCH 09/26] serial: atmel_serial: drop low-latency workaround

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Date:   Wed, 21 Apr 2021 11:54:52 +0200
From:   Johan Hovold <johan@...nel.org>
To:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Cc:     Jiri Slaby <jirislaby@...nel.org>, linux-serial@...r.kernel.org,
        linux-kernel@...r.kernel.org, Johan Hovold <johan@...nel.org>,
        Richard Genoud <richard.genoud@...il.com>
Subject: [PATCH 09/26] serial: atmel_serial: drop low-latency workaround

Commit 1ecc26bd2789 ("atmel_serial: split the interrupt handler") worked
around the infamous low_latency behaviour of tty_flip_buffer_push() by
dropping and reacquiring the port lock in the tasklet callback.

Since commit a9c3f68f3cd8 ("tty: Fix low_latency BUG"),
tty_flip_buffer_push() always schedules a work item to push data to the
line discipline and there's no need to keep any low_latency hacks around.

Cc: Richard Genoud <richard.genoud@...il.com>
Signed-off-by: Johan Hovold <johan@...nel.org>
---
 drivers/tty/serial/atmel_serial.c | 18 ------------------
 1 file changed, 18 deletions(-)

diff --git a/drivers/tty/serial/atmel_serial.c b/drivers/tty/serial/atmel_serial.c
index a24e5c2b30bc..058886d9045b 100644
--- a/drivers/tty/serial/atmel_serial.c
+++ b/drivers/tty/serial/atmel_serial.c
@@ -1178,13 +1178,7 @@ static void atmel_rx_from_dma(struct uart_port *port)
 			       1,
 			       DMA_FROM_DEVICE);
 
-	/*
-	 * Drop the lock here since it might end up calling
-	 * uart_start(), which takes the lock.
-	 */
-	spin_unlock(&port->lock);
 	tty_flip_buffer_push(tport);
-	spin_lock(&port->lock);
 
 	atmel_uart_writel(port, ATMEL_US_IER, ATMEL_US_TIMEOUT);
 }
@@ -1576,13 +1570,7 @@ static void atmel_rx_from_ring(struct uart_port *port)
 		uart_insert_char(port, status, ATMEL_US_OVRE, c.ch, flg);
 	}
 
-	/*
-	 * Drop the lock here since it might end up calling
-	 * uart_start(), which takes the lock.
-	 */
-	spin_unlock(&port->lock);
 	tty_flip_buffer_push(&port->state->port);
-	spin_lock(&port->lock);
 }
 
 static void atmel_release_rx_pdc(struct uart_port *port)
@@ -1667,13 +1655,7 @@ static void atmel_rx_from_pdc(struct uart_port *port)
 		}
 	} while (head >= pdc->dma_size);
 
-	/*
-	 * Drop the lock here since it might end up calling
-	 * uart_start(), which takes the lock.
-	 */
-	spin_unlock(&port->lock);
 	tty_flip_buffer_push(tport);
-	spin_lock(&port->lock);
 
 	atmel_uart_writel(port, ATMEL_US_IER,
 			  ATMEL_US_ENDRX | ATMEL_US_TIMEOUT);
-- 
2.26.3